Reactance tube circuit



Sept. 15, 1953 w. R. RAMBO REACTANCE TUBE CIRCUIT Filed NOV. 27, 1945 mm mum? WW APPLIED R-F VOLETAGE GRID BIAS c gfiawg MODULATING VOLETAGE VOLTAGE I INVENTOR 7 WILLIAM R. RAMBO ATTORNEY Patented Sept. 15, 1953 REACTANCE TUBE CIRCUIT William R. Rambo, Cambridge, Mass, assignor to the United States of America as represented by the Secretary of War Application November 27, 1945, Serial No. 631,186

6 Claims.

This invention relates generally to an electrical circuit and more particularly to a reactance tube.

In one method of frequency control the platecathode circuit of the reactance tube is shunted across the tuned circuit of a radio frequency oscillator. The control grid of the reactance tube is supplied, in this arrangement, with an alternating voltage, Eg derived from, but 90 out of phase with respect to, the radio frequency signal, E1, existing across the tank circuit. An amplified alternating voltage, E2, that is 90 out of phase with the alternating voltage, E1 across the tank circuit is produced in the plate circuit of the reactance tube. The reactance tube thereby acts as a shunting reactance to an extent which depends upon the amplification of the reactance tube. The amplification of the reactance tube may be controlled by the bias voltage applied to its control grid.

In an ideal reactance tube, the plate current can be considered in two principal portions, a D.-C. component, Inc, and a fundamental fre quency component, I1. The frequency-chang ing effect is determined by the reactive voltamperes controlled in the tube, the reactive voltamperes being calculated as the product of the fundamental-frequency plate current component and the applied radio frequency voltage, E1 I1. The principal energy dissipated at the plate is given by the product of the D.-C'. plate current component and the reactance tube plate supply voltage, ED.-c. In. o.

It is an object of this invention to reduce the plate dissipation associated with a reactance tube.

Gther objects, features and advantages of this invention will suggest themselves to those skilled in the art and will become apparent from the following description of the invention.

Fig. 1 is a schematic block diagram of a circuit setting forth the principles of this invention;

Fig. 2 is a set of graphs which will be used to explain the operation of this circuit; and

Fig. 3 is a schematic circuit diagram of a more complete embodiment of the invention illustrated in Fig. 1.

In the operation of a reactance tube accord ing to the present invention, the instantaneous electrical angle during which plate current flows is reduced considerably below the period of the radio frequency signal applied across the plate and cathode. With this purpose in View, means will be set forth to enable class C operation of the reactance tube.

In setting forth the principles of this invention, reference will be made first to Fig. 1. Cath ode I l of reactanoe tube It is connected to ground potential. Plate l2 of reactance tube it receives the applied radio frequency voltage E1 from the oscillator tank circuit plus the plate supply voitage E11-c. To control grid 13 of. reactance tube in is applied the grid bias voltage Ec, a modulating voltage Em plus the radio frequency driving voltage Eg which is displaced in phase substantially with respect to the radio frequency signal E1.

In explaining the operation of this circuit reference will now be made to Fig. 2 in which the voltage-current phase relations for class C oper ation of an ideal reactance tube are shown. The applied radio frequency potential E1 taken from the oscillator tank circuit is shown by the sinusoidal curve E1 in the graph 25 of Fig. 2. The reactance tube plate supply voltage is shown by the straight line ED.-C. in graph 2%. The radio frequency signal E1 is symmetrically centered about the plate upply voltage En-c.

The negative bias voltage applied to the control grid of the reactance tube is shown by the straight line designated -Ec in graph ii of Fig. 2. The cutoff potential of the reactance tube is shown by the line marked -Eco in graph 2! of Fig. 2. For class C operation, the grid bias voltage Ec is adjusted to be more negative than the cutoff potential Eco. The ratio frequency driving voltage applied to the grid of the reactance tube is shown by the sinusoidal curve E3 in graph 2| of Fig. 2. The grid driving voltage E; is symmetrically centered about the negative grid bias voltage E. The grid driving voltage Eg is displaced in phase by 90 with respect to the radio frequency signal E1 taken from the oscillator tank circuit and applied across the plate and cathode of the reactance tube.

Plate current will flow when the grid driving voltage Eg drives the grid above the cutofi potential Eco. The variation in the plate current is indicated by the pulses shown in graph of Fig. 2. The duration of the current pulses is shown by the angle 0 in graph 22 of Fig. 2. it can be seen that the pulses of plate current occur during a small fraction of the radio frequency cycle, their duration depending upon the amplitude of the grid driving voltage Eg and the grid bias potential Ec.

The fundamental frequency component of the plate current pulses will be defined I1 as before. The D.C. plate current component of the plate current pulses will be defined as Inc as before. The frequency-changing effect which has been defined as E1 I1 will increase for a given plate dissipation as the angle of plate current flow is reduced. This fact is shown in an article written by F. E. Terman and Wilbar C. Roake entitled Calculations and Design of Class C Amplifiers, published in the Proceedings of the I. R. volume 24, April 19, 1936, page 620.

The ratio of I1/In. o. will be greatly increased, providing the reduction in plate dissipation ED.-c. ID.-c. without adversely influencing the frequency-changing effect, E1 Ii, of the reactance tube.

It should be noted that the minimum value of E1 need not be maintained equal to or greater than the maximum driving voltage E' as in amplifier operation, since these two voltages occur 90 out of phase with each other. It is possible to drive the instantaneous plate voltage to zero or even to negative values as long as suitable positive plate voltage exists during the normal angle 0 of plate current fiow. This can be done by lowering the D.-C. plate supply voltage, En.-c., to a value even less than the negative peak of the radio frequency plate voltage swing E1. Plate dissipation En.-c. ID.-c. is thereby reduced while the reactive energy controlled by the tube is not affected as long as the plate current I1 and the applied R. F. voltage E1 remains constant. The amount of reduction in En.-c. is limited by the angle of plate current flow, 0, and in most practical cases the D.-C. plate supply voltage is set only slightly less than the peak value of the radio frequency voltage E1 in the tank circuit.

In some applications it may be necessary to modulate the reactance tube. This may be done in the grid circuit in a manner similar to the grid modulation of a class C amplifier. This type of circuit is particularly adapted to effect wide band modulation of power oscillators where reactance tube dissipation is an important factor.

A more detailed showing of the invention above described is contained in Fig. 3, in which electron tube to functions as a conventional oscillator, the operating frequency of which is determined by the tank circuit comprising inductance 3! and capacitance 32. The reactance tube circuit comprises electron tube 33, between the anode and cathode of which is applied the output of the tank circuit. A portion of this output is also applied through a blocking condenser 34 to a 90 phase shifting circuit comprising resistor 35 and capacitor 36 connected in series. Since the resistance is large compared to the capacity, the potential across the capacitor is substantially 90 phase displaced relative to the input potential, and this phase displaced potential is applied between grid and cathode of tube 33. This causes the oscillating plate current in tube 33 to be 90 phase displaced with respect to the oscillating voltage at its anode. By virtue of this current, tube 3.3 simulates a reactance across the tank circuit. As thus far described, the circuit is substantially conventional and substantially as disclosed in Smith Patent No. 2,248,132. For purposes of this invention any equivalent reactance tube circuit may be used.

As explained in connection with Fig. l, in accordance with the present invention, the grid of tube 33 is normally biased substantially below plate current cutoff by a fixed negative grid bias from a source of potential 31. The extent of this bias relative to the peak oscillating potential applied to grid from the tank circuit is such that space current normally flows only during a fraction of each cycle of said oscillating potential. It will be seen that by varying the bias applied to the grid, the magnitude of this fraction will vary and this results in variation of the reactive current injected into the tank circuit. If this variation in bias is accomplished by means of a modulation signal source 38 which, through a transformer 39, applies a varying bias to the grid in series withbias source 31, then the amount of reactive current reflected across the tank circuit will vary as a function of the signal voltage, and wavelength modulation of the tank circuit will result. The steady grid bias voltage from source 31 is preferably of such magnitude that space current will normally flow for less than one half of each cycle of theoscillating potential applied from the tank circuit to the grid in the absence of any signal voltage.

The present invention may be used in automatic frequency control systems such as the one described in an article by C. Travis entitled Automatic Frequency Control, Proceedings I. R. E., volume 23, October 1935, page 1125, to improve the performance thereof. An automatic frequency control circuit may be used to bring the signal carrier in a superheterodyne type radio receiver precisely to the center of its intermediate frequency band and locking it there.

While there has been described What is at present considered to be the preferred embodiment of this invention, it will beobvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention.

What is claimed is:

1. In combination, a circuit having oscillatory energy flowing therein, and means for injecting reactive current into said circuit during only a fraction of each cycle of said oscillatory energy, said means comprising electron tube means having input and output electrodes, means coupling said output electrodes to said circuit, means applying oscillatory energy to said input electrode approximately phase-displaced relative to the energy flowing in said circuit, means biasing one of said electrodes to normally render said electron tube means conductive only during a portion of each cycle oscillatory energy applied thereto from said circuit and for preventing conduction during the remainder of each cycle, and means to varythe potential on one of said electrodes thereby to vary the magnitude of said portion in accordance with the magnitude of said potential.

2. In combination, an oscillation generator having a resonant tank circuit and means for injecting reactance into said tank circuit only during a fraction of each cycle of said oscillation generator, said means comprising a single electron tube means connected to said tank circuit for injecting reactance effectively in parallel with said tank circuit, means normally biasing said electron tube means below space curr nt cutoff to such an extent that said electron tube means is rendered conducting only during a portion of each cycle of said oscillation generator, whereby the resistive load on said tank circuit is reduced, and means adapted to be controlled by a signal to vary the magnitude of the portion of each cycle during which said electron tube is rendered conducting to vary the amount of reactance elfectively injected into said tank circuit, whereby the frequency thereof is modulated in accordance with said signal.

3. Apparatus for producing wide band frequency modulation comprising a radio frequency oscillator having a resonant tank circuit and means for injecting reactance effectively in parallel with said tank circuit only during a fraction of each cycle of oscillation of said tank circuit to modulate the frequency of said oscillator, said means including an electron tube having an anode, cathode, and control grid, said anode and cathode being connected across at least a portion of said tank circuit through the anode cathode space of said electron tube, means for impressing between said cathode and control grid a potential which is approximately in quadrature with the potential impressed between said cathode and anode, means including a source of modulation voltage connected to the control grid for rendering the said electron tube conductive during a fraction of each cycle of the oscillator and for varying the said fraction in accordance with the value of the said modulation voltage, whereby reactance is injected effectively in parallel with said tank circuit during said fraction of each cycle to thereby vary the frequency of the oscillator in accordance with said modulation voltage.

a. In a timing modulation system for a circuit including reactive means and means for exciting said reactive means with radio frequency energy: first means coupled to said reactive means and responsive to said radio frequency energy for effectively changing the magnitude of said reactive means from a first value to a second value during only a portion of each cycle of said radio frequency energy in the absence of a modulating signal, a source of modulating signal, and second means coupled to said first means for varying the duration of said portion in accordance with the instantaneous amplitude of said modulating signal 5. A timing modulation system comprising an oscillator for generating radio frequency energy, said oscillator including frequency determining means therein, a reactance producing means, first means coupled to said frequency determining means and to said reactance producing means for eifectively coupling said reactance producing means to said frequenc determining means during only a portion of each cycle of said radio frequency energy in the absence of a modulating signal, a source of modulating signal, and second means coupled to said first means for varying the duration of said portion in accordance with the instantaneous amplitude of said modulating signal.

6. In combination, a circuit having oscillatory energy flowing therein, and means for injecting reactive current into said circuit during only a fraction of each cycle of said oscillatory energy, said means comprising electron tube means hav ing input and output electrodes, means coupling said output electrodes to said circuit, means applying oscillatory energy to said input electrode approximately phase-displaced relative to the energy flowing in said circuit, means biasing one of said electrodes to render said electron tube means conductive only during a portion of each cycle oscillatory energy applied thereto from said circuit and for preventing conduction during the remainder of each cycle, and signal controlled means for varying the bias on one of said electrodes thereby to vary the magnitude of said portion in accordance with the magnitude of a modulating signal impressed on said electron tube.

WILLIAM R. RAMBO.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,248,132 Smith July 8, 1941 2,294,372 Barton Sept. 1, 1942 2,341,655 Roberts Feb. 15, 1944 2,342,708 Usselman Feb. 2 1944 2,494,795 Bradley Jan. 17, 1950 OTHER REFERENCES Terman Roake: I. R. E. Proceedings, April 1936, pages 620-652. 

